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Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals

Abstract

The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.

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Figure 1: Singlet exciton fission and triplet transfer.
Figure 2: Numerical decomposition of transient optical absorption data.
Figure 3: Kinetics of triplet transfer.
Figure 4: Enhancement of photoluminescence from PbSe due to triplet transfer.

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Acknowledgements

M.T. thanks the Gates Cambridge Trust for financial support. B.E. thanks the KACST-Cambridge Research Project for support and Selwyn College, Cambridge for a Research Fellowship. B.J.W. was supported by a Herchel Smith Research Fellowship. M.L.B. was supported by Studienstiftung des Deutschen Volkes. A.R. thanks Corpus Christi College, Cambridge for a Research Fellowship. This work was supported by the EPSRC and the Winton Programme for the Physics of Sustainability.

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Contributions

M.T. prepared samples, performed time-resolved and steady-state optical measurements, analysed the data and wrote the paper. B.E. prepared and characterized the samples and wrote the paper. S.G. set up the multi-pass experiments. M.L.B. synthesized the nanocrystals. B.J.W. performed steady-state optical measurements. K.P.M. characterized the samples. N.C.G. supervised the work of M.L.B. R.H.F. supervised the work of M.T., S.G. and K.P.M. and wrote the paper. A.R. initiated and guided the work, set up the multi-pass experiments, performed time-resolved optical measurements and wrote the paper.

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Correspondence to Akshay Rao.

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The authors declare no competing financial interests.

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Tabachnyk, M., Ehrler, B., Gélinas, S. et al. Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals. Nature Mater 13, 1033–1038 (2014). https://doi.org/10.1038/nmat4093

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